This relates to a method and apparatus for routing message packets and, in particular, to a method and apparatus especially suited to routing message packets in massively parallel processors such as those disclosed in the above-referenced '471 and '474 applications and the '400 patent.
As shown in FIG. 1A of the '400 patent which is reproduced in FIG. 1, the computer system of those applications comprises a mainframe computer 10, a microcontroller 20, an array 30 of parallel processing integrated circuits 35, a data source 40, a first buffer and multiplexer/demultiplexer 50, first, second, third and fourth bidirectional bus control circuits 60, 65, 70, 75, a second buffer and multiplexer/demultiplexer 80, and a data sink 90. Mainframe computer 10 may be a suitably programmed commercially available general purpose computer such as a VAX (.TM.) computer manufactured by Digital Equipment Corp. Microcontroller 20 is an instruction sequencer of conventional design for generating a sequence of instructions that are applied to array 30 by means of a thirty-two bit parallel bus 22. Microcontroller 20 receives from array 30 a signal on line 26. This signal is a general purpose or GLOBAL signal that can be used for data output and status information. Bus 22 and line 26 are connected in parallel to each IC 35. As a result, signals from microcontroller 20 are applied simultaneously to each IC 35 in array 30 and the signal applied to microcontroller 20 on line 26 is formed by combining the signal outputs from all of ICs 35 of the array.
Array 30 contains thousands of identical ICs 35; and each IC 35 contains several identical processor/memories 36. In the embodiment disclosed in the '400 patent, it is indicated that the array may contain up to 32,768 (=2.sup.15) identical ICs 35; and each IC 35 may contain 32 (=2.sup.15) identical processor/memories 36. At the time of filing of this application for patent, arrays containing up to 4096 (=2.sup.12) identical ICs 35 containing 16 (=2.sup.4) identical processor/memories each have been manufactured and shipped by the assignee as Connection Machine (Reg. .TM.) computers.
Processor/memories 36 of the '400 patent are organized and interconnected in two geometries. One geometry is a conventional two-dimensional grid pattern in which the processor/memories are organized in a rectangular array and connected to their four nearest neighbors in the array. For convenience, the sides of this array are identified as NORTH, EAST, SOUTH and WEST. To connect each processor/memory to its four nearest neighbors, the individual processor/memories are connected by electrical conductors between adjacent processor/memories in each row and each column of the grid.
The second geometry is that of a Boolean n-cube. To understand the n-cube connection pattern, it is helpful to number the ICs from 0 to 32,767 (in the case of a cube of fifteen dimensions) and to express these numbers or addresses in binary notation using fifteen binary digits. Just as we can specify the position of an object in a two dimensional grid by using two numbers, one of which specifies its position in the first dimension of the two-dimensional grid and the other which specifies it position in the second dimension, so too we can use a number to identify the position of an IC in each of the fifteen dimensions of the Boolean 15-cube. In an n-cube, however, an IC can have one of only two different positions, 0 and 1, in each dimension. Thus, the fifteen-digit IC address in binary notation can be and is used to specify the IC's position in the fifteen dimensions of the n-cube. Moreover, because a binary digit can have only two values, zero or one, and because each IC is identified uniquely by fifteen binary digits, each IC has fifteen other ICs whose binary address differs by only one digit from its own address. We will refer to these fifteen ICs whose binary address differs by only one from that of a first IC as the first IC's nearest neighbors. Those familiar with the mathematical definition of a Hamming distance will recognize that the first IC is separated from each of its fifteen nearest neighbors by the Hamming distance one.
To connect ICs 35 of the above-referenced applications in the form of a Boolean 15-cube, each IC is connected to its fifteen nearest neighbors by 15 input lines 38 and fifteen output lines 39. Each of these fifteen input lines 38 to each IC 35 is associated with a different one of the fifteen dimensions of the Boolean 15-cube and likewise each of the fifteen output lines 39 from each IC 35 is associated with a different dimension. Specific details of the connection wiring for the Boolean n-cube are set forth in the '943 application referenced above.
To permit communication through the interconnection pattern of the Boolean 15-cube, the results of computations are organized in the form of message packets; and these packets are routed from one IC to the next by routing circuitry in each IC in accordance with address information that is part of the packet.
Each IC 35 contains a plurality of processor/memories that are disclosed in greater detail in FIG. 7A of the '400 patent and in FIGS. 4 and 6 of '090 application for "Massively Parallel Processor". As shown in FIG. 7A, processor/memory 36 comprises a random access memory (RAM) 250, an arithmetic logic unit (ALU) 280 and a flag controller 290. The inputs to RAM 250 include a message packet input line 122 from a communication interface unit (CIU) 180 of FIG. 6B of the '400 patent; and the outputs from RAM 250 are lines 256, 257 to ALU 280. The ALU operates on data from three sources, two registers in the RAM and one flag input, and produces two outputs, a sum output on line 285 that is written into one of the RAM registers and a carry output on line 287 that is made available to certain registers in the flag controller and can be supplied to communications interface unit 180 via message packet output line 123.
An alternative design for the processor/memory is disclosed in the '090 application for "Massively Parallel Processor". As shown in FIGS. 4 and 6 thereof, the processors and memories are located in separate integrated circuits 334, 340 mounted on the same circuit board In particular, each integrated circuit 334 comprises sixteen identical processors 336, a control unit 337, a router 338 and a memory interface 339. The memory interface connects the sixteen processors of an integrated circuit 334 to their memories which, illustratively, are located on sixteen separate integrated circuits 340. The router 338 connects the sixteen processors to twelve nearest neighbor routers connected in a twelve dimension hypercube.
Each integrated circuit 35 also includes certain supervisory circuitry for the processor/memories on the IC and a routing circuit for connecting the IC to its nearest neighbor ICs in the Boolean n-cube. As disclosed in FIG. 6B of the '400 patent which is reproduced in FIG. 2, the supervisory circuitry comprises a timing generator 140, a programmable logic array 150 for decoding instructions received from microcontroller 20 and providing decoded instructions to the processor/memories of the IC, and a communications interface 180 which controls the flow of outgoing and incoming message packets between the processor/memories of an IC and routing circuit associated 200 with that IC.
Routing circuit 200 controls the routing of message packets to and from nearest neighbor ICs in the Boolean n-cube. It comprises a line assigner 205, a message detector 210, a buffer and address restorer 215 and a message injector 220 connected serially in this order in a loop so that the output of one element is provided to the input of the next and the output of message injector 220 is provided to line assigner 205.
Line assigner 205 analyzes the addresses of message packets received on incoming lines 38 to determine whether they are directed to this particular IC or some other IC; it routes the message packets toward their destination if possible; and it stores any message packet destined for this IC as well as any message packet that cannot be routed on because of a conflict in circuit allocation. Line assigner 205 comprises a fifteen by fifteen array of substantially identical routing logic cells 400. Each column of this array controls the flow of message packets between a nearest neighbor routing circuit 200 in one dimension of the Boolean 15-cube. Each row of this array controls the storage of one message packet in routing circuit 200.
Message detector 210 checks for the receipt of message packets, examines the address of the message packets received on lines 207 from line assigner 205 and supplies those message packets addressed to this IC to communications interface 180 Buffer and address restorer 215 comprise a tapped shift register The output of the buffer and address restorer is applied to the message injector 220. Message injector 220 injects a single message packet at a time from communications interface 180 into the group of message packets circulating through the routing circuit.
Signals from the routing circuit are applied to CIU 180 on lines 197, 198 and 199. These signal lines provide, respectively, an indication whether an incoming message packet is available from the routing circuit, the incoming message packet itself and an indication whether the outgoing message packet on line 196 was successfully received by the routing circuit. A signal on line 194 indicates when a message packet is available for routing and the message packet itself is provided on line 196.
If no routing conflicts are encountered, a message packet will be routed from an input to a routing cell of the first dimension to the register in the processor/memory to which it is addressed during one message cycle. If there are routing conflicts, the message packet will be temporarily stored in the processing and storage means of a routing circuit at one or more intermediate points; and more than one routing cycle will be required to route the message packet to its destination.